We plan to use the defective interfering particles (DI) of vesicular stomatitis virus (VSV) to study the processes of viral RNA replication, transcription and inteference. We would like to determine, in addition, how these processes are regulated by host factors during the infection of a given mammalian cell. The DI particles are essentially deletion mutants of VSV which are unable to transcribe but do replicate in vivo in the presence of the helper virus. This, by utilizing DI particles one has experimental conditions where replication can be examined largely independently of transcription. We will characterize the virus-specific RNA and protein components of intracellular viral DI nucleocapsids which are required for replication and determine if these components are related to those components involved in VSV transcription. The ultimate goal of these experiments is the establishment of an in vitro replication system for the synthesis of new progeny RNA. This should facilitate the important studies of how DI particles interfere with the replication of the wild type virus and what their role is in the establishment of persistent infections. We are interested in beginning to probe the role of possible host factors in VSV replication. The involvement of host factors in VSV replication is suggested by the existence of certain host range mutants of VSV and of naturally restrictive host cell lines. We plan to study whether host proteins are associated with VSV replication complexes. An alternative approach to understand the role of non-VSV encoded factors will be to study the mechanism by which poxviruses are able to overcome the host restriction of wild type VSV replication that occurs in rabbit cornea cells.